This invention relates to a method and apparatus for laying a sheet of material on a surface, and is particularly concerned with the laying of such sheet material having a naturally sticky or tacky texture.
One such material consists of a pre-impregnated fibre-reinforced material by which we mean a material comprising a layer of woven, unidirectional or random fibres impregnated with a thermo-setting resin. Such materials are now widely used due to their high strength to weight ratio and the relative ease by which complex shapes can be made using appropriate mould or forming tools, and find particular application in the aircraft industry for example in the manufacture of helicopter rotor blades.
It has been proposed to implement such manufacture by way of automated manufacturing techniques whereby sheets of the material are first cut to shape on a cutting table, then transported robotically from the table and laid on the surface of a mould tool in a predetermined sequence.
Difficulty has been experienced in such an operation since the natural tackiness of the sheet of material due to the resin has caused problems, especially in transferring the sheet of material from a transfer tool onto the mould surface.
In an alternative manufacturing technique known as tape laying, a continuous narrow tape of pre-impregnated fibre-reinforced material is laid directly on to the concave surface of the mould tool. This requires very sophisticated and expensive computer controlled equipment and is not always entirely satisfactory especially for very complex shapes.
Consequently in this specification the use of the term "sheet" is intended to include a sheet cut from a roll of material and a sheet made up of a plurality of adjacently laid narrow tapes.